Nuclear power plants and other heat-generating power plants, such as coal, oil and gas power plants, are normally equipped with a circulation system for water, in which steam, which is generated in a reactor vessel or in a steam generator connected thereto, is passed to a steam turbine, from there to a condenser and condensate formed therein, after cleaning in a condensate cleaning filter and preheating, is returned to the reactor vessel or the steam generator. For the cleaning of the condensate, normally ion exchange resin is used.
In operation of power plants of the kinds mentioned above various corrosion products are formed in the circulation system, inter alia in the form of oxides containing one or several metals of the kinds included in construction material in the circulation system, such as, above all, iron, further, inter alia, nickel, cobalt, chromium, copper, titanium, molybdenum, zinc and zirconium. In the event that a nuclear reactor vessel is included in the circulation system, the corrosion products will be radioactive. In addition, impurities may enter the circulation system through leakage. When cleaning the water in the condensate cleaning filter with ion exchange resin, corrosion products and other impurities are captured by the ion exchange resin.
A condensate cleaning filter in the form of an ion exchange resin often comprises a chamber containing a plurality of filter elements, each one consisting of a liquid-permeable support matrix and a layer, generated thereon in the chamber, of finely divided particles of an organic ion exchange resin ("precoat filter"). The layer of the ion exchange resin may be applied on the support matrix by arranging the filter in a liquid circulation system and supplying to the liquid a suspension of the ion exchange resin while the liquid is circulated in the circulation system. This circulation system is used only for preparation of the filter by coating the support matrix with the ion exchange resin.
When a condensate cleaning filter of the above-mentioned kind has been in service for a certain period of time, the ion exchange resin is removed, usually by backwashing, and is replaced with a new ion exchange resin.
When cleaning the water, ionic corrosion products of a non-colloidal nature, as well as any other ionic impurities of a non-colloidal nature, are captured by the ion exchange resin and penetrate into the interior of the grains of the ion exchange resin, whereas colloidal corrosion products and any other colloidal impurities are successively collected on the surface of the ion exchange resin grains and block an increasingly greater part of the electrical charge of the ion exchange resin, so that its ability to fulfill its primary task of rendering the mentioned ionic substances harmless is increasingly deteriorated, while at the same time the packing density of the layer of ion exchange resin increases and hence the pressure drop across the filter. This process, in order for the condensate cleaning filter to have the prescribed cleaning effect and to provide a sufficiently low pressure drop, results in the ion exchange resin having to be replaced by new ion exchange resin without the used ion exchange resin being at all fully consumed.
According to the present invention, a drastic reduction of the consumption of ion exchange resin is obtained, while at the same time the process for the coating of the support matrices of the condensate cleaning filter is eliminated.